Refrigeration system with reverse flow defrost

Abstract

A refrigeration system including a compressor operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet. A second heat exchanger is disposed adjacent a cool space. A valve is movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.

1 . A refrigeration system comprising: 
 a compressor operable to discharge compressed refrigerant;    a first heat exchanger operable to cool the compressed refrigerant, the first heat exchanger including a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet;    a second heat exchanger disposed adjacent a cool space; and    a valve movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.    
   
   
       2 . The refrigeration system as set forth in  claim 1  wherein the compressor comprises an oil-flooded screw compressor.  
   
   
       3 . The refrigeration system as set forth in  claim 1  wherein the compressor comprises a plurality of compressors, each compressor operable to discharge compressed refrigerant to a common header.  
   
   
       4 . The refrigeration system as set forth in  claim 1  wherein the second heat exchanger comprises a plurality of evaporators.  
   
   
       5 . The refrigeration system as set forth in  claim 4  wherein each of the plurality of evaporators is in selective fluid communication with a liquid header and a suction header.  
   
   
       6 . The refrigeration system as set forth in  claim 4  further comprising a plurality of defrost valves, each defrost valve positioned to provide selective fluid communication between a hot gas header and one of the plurality of evaporators.  
   
   
       7 . The refrigeration system as set forth in  claim 6  wherein each of the plurality of defrost valves comprises a solenoid-actuated valve.  
   
   
       8 . A refrigeration system comprising: 
 a plurality of compressors, each compressor operable to discharge compressed refrigerant;    a first heat exchanger operable to cool the compressed refrigerant, the first heat exchanger comprising a first inlet, an outlet, and a second inlet between the first inlet and the outlet;    a plurality of evaporators;    a receiver in fluid communication with the first heat exchanger and in selective fluid communication with each of the plurality of evaporators;    a hot gas header;    a valve movable between a first position to direct the compressed refrigerant to the first inlet and a second position to direct the compressed refrigerant to the hot gas header; and    a plurality of defrost valves, each defrost valve movable between a first position to place the receiver in fluid communication with one of the plurality of evaporators to cool the evaporator and a second position to place the hot gas header in fluid communication with the one of the plurality of evaporators to heat the evaporator, the evaporator discharging refrigerant to the second inlet when the defrost valve is in the second position.    
   
   
       9 . The refrigeration system as set forth in  claim 8  wherein each of the compressors comprises an oil-flooded screw compressor.  
   
   
       10 . The refrigeration system as set forth in  claim 8  wherein each of the plurality of evaporators is in selective fluid communication with a liquid header and a suction header.  
   
   
       11 . The refrigeration system as set forth in  claim 8  wherein at least one of the plurality of defrost valves is positioned in the first position when another of the plurality of defrost valves is in the second position.  
   
   
       12 . The refrigeration system as set forth in  claim 8  wherein each of the plurality of defrost valves comprises a solenoid-actuated valve.  
   
   
       13 . A method of operating a refrigeration system comprising: 
 operating a compressor to deliver compressed refrigerant;    directing the compressed refrigerant to a first inlet of a first heat exchanger;    condensing the compressed refrigerant within the first heat exchanger;    expanding a portion of the compressed refrigerant;    passing the portion of the expanded compressed refrigerant through a second heat exchanger to cool the heat exchanger;    manipulating a valve to redirect the compressed refrigerant to the second heat exchanger to heat the second heat exchanger; and    directing the compressed refrigerant to a second inlet of the first heat exchanger, the second inlet disposed downstream of the first inlet.    
   
   
       14 . The method as set forth in  claim 13  wherein operating the compressor comprises operating at least one of a plurality of compressors to deliver compressed refrigerant to a common header.  
   
   
       15 . The method as set forth in  claim 13  wherein the second heat exchanger comprises a plurality of evaporators.  
   
   
       16 . The method as set forth in  claim 15  wherein at least one of the plurality of evaporators is cooled and at least one of the plurality of evaporators is heated simultaneously.  
   
   
       17 . The method as set forth in  claim 15  further comprising separating the portion of compressed refrigerant into a plurality of flow streams and expanding each stream.  
   
   
       18 . The method as set forth in  claim 15  wherein the manipulating step redirects at least a portion of the compressed refrigerant to a hot gas header.  
   
   
       19 . The method as set forth in  claim 18  further comprising actuating at least one of a plurality of defrost valves to direct compressed refrigerant from the hot gas header to at least one of the evaporators.  
   
   
       20 . The method as set forth in  claim 13  further comprising directing the compressed refrigerant to the first heat exchanger after passing the compressed refrigerant through the second heat exchanger.